Preheat the oven to 350°F. On a lightly floured work surface, roll out the first disc of pie dough (prepackaged crusts normally have 2). Roll out into a thin rectangular shape. Using a pizza cutter, cut a large rectangle out of the middle, then cut that into 6 equally sized squares. Do the same with your 2nd disc of pie dough. You should have 12 equal squares. Place 6 of them on a baking sheet lined with parchment paper or a silicone baking mat.

Whisk together the egg and milk and brush that over the dough squares. For the filling, mix together the brown sugar, cinnamon and flour in a separate small bowl. Place a tablespoon of sugar mix onto each square and spread to within 1/4 inch of the border of the dough square.

Once you have filling on each of the 6 squares, brush the remaining 6 pastry squares with egg wash and place them on top of the squares with the filling. Place them with the egg wash side down. Use your fingers to pinch and seal around the edges, then go back around them with a fork. Then use the fork (or a toothpick) to prick holes over the top of the pastries. Brush egg wash over the tops.

Bake for about 6 minutes, then rotate the pan and bake an additional 6 minutes or until lightly golden. Once they're done, let them cool on the pan for 5 or so minutes, then carefully transfer them to a wire rack to cool completely.

Make the frosting by whisking together the confectioners sugar, cinnamon, vanilla and milk. Once the poptarts are cooled, use a spoon to glaze the top of them, leaving space around the edges. Within a few hours, the frosting will harden. Store them in an airtight container. To reheat them, don't put them into a toaster! Just pop them in the microwave for 10-15 seconds.